The present invention relates to a solid titanium catalyst component useful for producing a polyolefin, a process for preparing the solid titanium catalyst component, an olefin polymerization catalyst containing the catalyst component and an olefin polymerization process using the catalyst.
Ziegler-Natta catalysts comprising a titanium catalyst component and an organoaluminum compound have been conventionally widely used as catalysts for preparing polyolefins. Above all, catalysts containing a carrier supported solid titanium catalyst component as the titanium catalyst component are known to show high polymerization activities.
It is also known that catalysts containing a magnesium chloride supported titanium catalyst component show high polymerization activities and produce polyolefins of high stereoregularity when olefins such as propylene and butene are polymerized.
Further, there have been proposed various catalysts capable of producing polyolefins of much higher stereoregularity. For instance, there has been proposed a catalyst containing an electron-donative compound (electron donor) as a third component together with a magnesium chloride supported solid titanium catalyst component and an organoaluminum component.
In the polymerization of an olefin using a catalyst containing such a solid titanium catalyst component, however, there is a problem that a polyolefin of low stereoregularity is produced as a by-product in addition to the polyolefin of high stereoregularity. Moreover, there is a limitation on decrease of the amount of the polyolefin of low stereoregularity even if a catalyst for preparing a polyolefin of high stereoregularity, that contains the electron donor as a third component, is used.
The solid titanium catalyst component is prepared by bringing a titanium compound, a magnesium compound, an electron donor, etc. into contact with each other. In the solid titanium catalyst component thus prepared, a surplus titanium compound that causes production of the polyolefin of low stereoregularity is contained. In order to produce a polyolefin of high stereoregularity, the solid titanium catalyst component is desired to contain no surplus titanium compound.
It is known that the surplus titanium compound can be partly eliminated when the solid titanium catalyst component is washed with hexane at room temperature. Further, there has been proposed a process for preparing a solid titanium catalyst component in which the surplus titanium compound is removed from the solid obtained by contacting a titanium compound, a magnesium compound, an electron donor, etc., by the use of a solvent. For instance, Japanese Patent Laid-Open Publication No. 124909/1984 describes that the surplus titanium compound can effectively be washed out with an aromatic hydrocarbon such as toluene.
However, when the solid titanium catalyst component is washed with the aromatic hydrocarbon as described above, the electron donor is also removed together with the surplus titanium compound, and as a result the solid titanium catalyst component cannot exert its full effects to decrease the quantity of the polyolefin of low stereoregularity.
Accordingly, there has been desired development of a solid titanium catalyst component and a catalyst containing it, which can produce a polyolefin of high stereoregularity with high activities as well as in a decreased quantity of a polyolefin of stereoregularity.
The present invention has been made under such circumstances as described above, and it is an object of the invention to provide a solid titanium catalyst component capable of decreasing the quantity of a polyolefin of low stereoregularity as a by-product and producing a polyolefin of high stereoregularity with high activities. It is another object of the invention to provide a process for preparing the solid titanium catalyst component. It is a further object of the invention to provide an olefin polymerization catalyst containing the solid titanium catalyst component, and an olefin polymerization process using the olefin polymerization catalyst.
The solid titanium catalyst component according to the invention comprises magnesium, titanium, halogen and an electron donor and has the following properties:
(1) the titanium content is not more than 2.5% by weight,
(2) the total content of magnesium and halogen is at least 65% by weight and less than 92% by weight,
(3) the electron donor content is in the range of 8 to 30% by weight,
(4) the weight ratio of the electron donor to titanium is in the range of 7 to 40, and
(5) the solid titanium catalyst component is substantially free from elimination of titanium when washed with hexane at room temperature and has a titanium content decrease ratio of less than 15% by weight when washed with o-dichlorobenzene at 90xc2x0 C.
The process for preparing a solid titanium catalyst component according to the invention comprises bringing
(i) solid titanium which comprises magnesium, titanium, halogen and an electron donor and is free from elimination of titanium when washed with hexane at room temperature, into contact with
(ii) a polar compound having a dipole moment of 0.50 to 4.00 Debye at a temperature of at least 40xc2x0 C. to decrease the titanium content in the solid titanium (i) by at least 25% by weight, so as to prepare a solid titanium catalyst component having a weight ratio of the electron donor to titanium of at least 7.
The polar compound having a dipole moment of 0.50 to 4.00 Debye is preferably a halogen-containing aromatic hydrocarbon.
It is preferred that the solid titanium (i) used in the contact with the polar compound having a dipole moment of 0.50 to 4.00 Debye (ii) has a weight ratio of the electron donor to titanium of not more than 6.
The solid titanium (i) is preferably a solid (1) obtained by bringing (a) a magnesium compound in a liquid state, (b) a titanium compound in a liquid state and (c) an electron donor into contact with each other. This solid titanium (i) may be a solid (2) obtained by further bringing the solid (1) into contact with (b) the titanium compound in a liquid state.
The olefin polymerization catalyst according to the invention comprises (A) the solid titanium catalyst component, (B) an organometallic compound and (C) an organosilane compound having at least one alkoxy group.
Another olefin polymerization catalyst according to the invention is a prepolymerized catalyst obtained by prepolymerizing or precopolymerizing an olefin onto (A) the solid titanium catalyst component described above, (B) an organometallic compound, and optionally, (C) an organosilane compound having at least one alkoxy group.
In the present invention, the olefin polymerization catalyst may be the above-described prepolymerized catalyst alone, or optionally in combination with (B) an organometallic compound and/or (C) an organosilane compound having at least one alkoxy group.
The olefin polymerization process according to the invention comprises polymerizing or copolymerizing an olefin in the presence of any one of the above-described olefin polymerization catalysts. In this process, the olefin can be polymerized with high activities. Moreover, a polyolefin of high stereoregularity can be produced in a decreased quantity of a polyolefin of low stereoregularity produced.